Distinguishing Low and High Water Consumers-A Paradigm of Disease Risk

Abstract

A long-standing body of clinical observations associates low 24-h total water intake (TWI = water + beverages + food moisture) with acute renal disorders such as kidney stones and urinary tract infections. These findings prompted observational studies and experimental interventions comparing habitual low volume (LOW) and high volume (HIGH) drinkers. Investigators have learned that the TWI of LOW and HIGH differ by 1-2 L·d^-1, their hematological values (e.g., plasma osmolality, plasma sodium) are similar and lie within the laboratory reference ranges of healthy adults and both groups appear to successfully maintain water-electrolyte homeostasis. However, LOW differs from HIGH in urinary biomarkers (e.g., reduced urine volume and increased osmolality or specific gravity), as well as higher plasma concentrations of arginine vasopressin (AVP) and cortisol. Further, evidence suggests that both a low daily TWI and/or elevated plasma AVP influence the development and progression of metabolic syndrome, diabetes, obesity, chronic kidney disease, hypertension and cardiovascular disease. Based on these studies, we propose a theory of increased disease risk in LOW that involves chronic release of fluid-electrolyte (i.e., AVP) and stress (i.e., cortisol) hormones. This narrative review describes small but important differences between LOW and HIGH, advises future investigations and provides practical dietary recommendations for LOW that are intended to decrease their risk of chronic diseases.

Keywords: arginine vasopressin; cortisol; dietary protein; dietary salt; plasma osmolality; thirst.

Figure 1

The hydration continuum. Perturbations of fluid-electrolyte variables initiate thirst and neuroendocrine responses to restore homeostasis and to maintain optimal health and function. The magnitude of a fluid-electrolyte deficit (DEFICIT) or fluid-electrolyte excess (EXCESS) determines the strength of responses that return volume, osmolality and pressure back to the encoded brain set point. Abbreviations: SNA, sympathetic nerve activity; AVP, arginine vasopressin; ANG II, angiotensin II; ALD, aldosterone; ANP, atrial natriuretic peptide. Revised from Armstrong & Johnson, 2018 [41].

Figure 2

The relationship between daily total water intake (all sources) and plasma AVP concentration, based on 11 published laboratory investigations. The plasma AVP threshold of 2 pg·mL⁻¹ [41] occurs at a TWI of 1.8 L·24 h⁻¹, which is approximately 64 total oz of water per day. Low volume drinkers and water-deprived adults appear as the 5 data points above the plasma AVP threshold. See text for details. The range of adequate intakes for women and men appear as zone A (European Food Safety Authority [10]) and zone B (U.S. National Academy of Medicine [11]).

Figure 3

Relationships of total water intake to urine volume (panel A) and urine osmolality (panel B), when low volume drinkers (LOW, n = 14–30 each symbol) and high volume drinkers (HIGH, n = 14–22) reversed their habitual 24-h TWI during two investigations. Open symbols represent study 1 [20] and closed symbols represent study 2 [21]. Arrows denote changes from baseline (pre-intervention) to day 3 or 4 of each modified TWI. The horizontal dashed line in Panel A and Panel B represent the urine values that exist when plasma AVP is 2.0 pg·mL⁻¹. Experimental design details appear in the footnotes of Table 1 and Table 2.

Figure 3

Relationships of total water intake to urine volume (panel A) and urine osmolality (panel B), when low volume drinkers (LOW, n = 14–30 each symbol) and high volume drinkers (HIGH, n = 14–22) reversed their habitual 24-h TWI during two investigations. Open symbols represent study 1 [20] and closed symbols represent study 2 [21]. Arrows denote changes from baseline (pre-intervention) to day 3 or 4 of each modified TWI. The horizontal dashed line in Panel A and Panel B represent the urine values that exist when plasma AVP is 2.0 pg·mL⁻¹. Experimental design details appear in the footnotes of Table 1 and Table 2.

Figure 4

Relationships among total water intake, osmolality, AVP and four hydration biomarkers of LOW (○●) and HIGH (□■). A small blood osmolality difference (LOW versus HIGH; panels A and B) results in the subsequent responses illustrated in panels B–F. The plasma AVP threshold of 2 pg·ml^-1 (see Section 3 above) is depicted as a dashed line in panels B-F. Open symbols represent study 1 [20] and closed symbols represent study 2 [21] baseline mean values (see columns 2 and 3 of Table 1). Arrows aid visual discrimination of LOW and HIGH values in studies 1 and 2. The blood osmolality reference range of laboratory values for healthy adults (panels A and B) is 285–295 mOsm·kg⁻¹ [47]. (A): the influence of TWI on blood osmolality; (B): the influence of blood osmolality on plasma AVP concentration; (C): the influence of plasma AVP on urine volume; (D): the influence of plasma AVP on urine osmolality; (E): the influence of plasma AVP on urine specific gravity; (F): the influence of plasma AVP on the ratio of urine osmolality-to-plasma osmolality.

Figure 5

Proposed series of events that lead to the differential risk of chronic diseases in LOW and HIGH. Homeostatic neuroendocrine responses include increased plasma AVP and cortisol in LOW (see Section 5 above). Abbreviations: TRR, top half of the laboratory reference range; BRR, bottom half of the laboratory reference range [42]. This paradigm is based on eight source publications [7,9,18,42,61,90,91,92].

Figure 6

Frequency distribution of the plasma osmolality (P_OSM) threshold for the onset of thirst. The horizontal gray zone represents the laboratory reference range of P_OSM values (285–295 mOsm·kg⁻¹) for healthy adults [47].

Figure 7

Relationships between 24-h renal osmolar excretion (ROE) and food energy, total water intake and urine volume. Each symbol represents a group mean (n = 14–682) from the six studies in Table 3. (A): the strong relationship between food energy and ROE; (B): the weak relationship between TWI and ROE; (C): as ROE increases, the obligatory urine volume increases.